1. Field of the Invention
The present invention relates to a method and device for the on-line testing (namely the testing during operation) of an antenna formed by a plurality of radiating sources.
A particular field of application of the invention relates to the antennas of monopulse type secondary radars, enabling the radiation in space of the pulses produced by an IFF (Identification Friend or Foe) interrogator and the picking up of responses, if any, from the interrogated aircraft. Antennas such as these are constituted by a plurality of radiating elements, called columns. It is very difficult to find out, on the spot, if one, or more of these columns is malfunctioning. Moreover, should there be a decline in the performance characteristics of the antenna, it is not possible to localize the column or columns in question with precision.
2. Description of the Prior Art
A known practical method of localizing the columns consists in placing a detector successively before each column to ascertain that the radiation from these columns is really that expected. The drawback of such a method lies in the interaction of the radiation patterns of the columns neighboring the tested column, which gives low precision to the measurements made. Furthermore, this method calls for the temporary stoppage of the antenna in its functions of interrogation and of receiving responses from aircraft.
There also exist various methods that work directly on the radiation pattern of the antenna and are based on the following principles:
the mean level of the minor lobes may enable the detection of a malfunction. In fact, this method is ruled out for it does not enable the extraction of a reliable information element relating to the end columns for which the variations of the mean level on the minor lobes are too small; PA1 the characteristic function of the alignment of the dipoles gets cancelled as many times as there are radiating elements in the alignment. The observation of the number of zeros should therefore enable the detection of malfunctions. However, in practice, this is an unreliable method in the sense that, in practice, reflections on obstacles may cause the zeros to disappear; PA1 the radiation pattern of an antenna is deduced from the Fourier transform of the illumination of this antenna. In computing the reverse Fourier transform, it should therefore be possible to reconstitute the aspect of the illumination of the antenna and thus detect holes at the position of the malfunctioning columns. In fact, this information cannot be exploited for it is not possible to recover the essential information of the signal, namely its phase. PA1 constituting a library of radiation patterns of the antenna, firstly when all the radiating sources work normally and, secondly, when at least one of said sources is deliberately put into a state of malfunctioning; PA1 measuring the radiation pattern of the antenna during its on-site operation PA1 computing the coefficient of correlation of said radiation pattern with each of the radiation patterns contained in said library; PA1 computing the maximum value of the coefficient of correlation so as to detect a malfunction, if any, in one or more of said radiating sources. PA1 first means for the measuring and memorizing, in a library, of the radiation patterns of the antenna, firstly when all the radiating sources work normally and, secondly, when at least one of said sources is deliberately put into a state of malfunctioning; PA1 second means to measure the radiation pattern of the antenna during its on-site operation; PA1 means to compute the coefficient of correlation of the radiation pattern of the antenna and of each pattern contained in said library; PA1 means to compute the maximum value of the coefficient of correlation to detect a malfunction if any.
The object of the invention is to overcome the above-mentioned drawbacks by proposing a method and a device for the on-site testing of the operation of a multiple-source antenna that enables the precise localizing of the malfunctioning radiation source or sources, without hampering the prime function of this antenna.
Although the description of the method and of the device according to the invention is made in the context of the application to a secondary radar antenna, it is important at the very outset to note that the invention is not limited to this particular application, as shall be seen hereinafter.